Spanners are frequently used in works. Generally, a spanner has a head for driving a screwing object. In some works, it is necessary to control the force applied to the screwing object so as to prevent the spanner or screwing object from damage or giving a proper engaging level to the screwing object so that it can be locked to an object properly. Thus electronic torque spanner is developed.
For example, U.S. Pat. No. 3,970,155 and No. 4,006,629 disclose the typical electronic torque spanners comprising a stain gauge installed at the neck portion of the spanner. When the force applies on the screwing objects, the strain at the neck portion will be measured by the stain gauge. And the signal will be transferred into the torque and shown on the display.
However, those prior arts still have a defect that the measured strain value will be smaller. The torque value will be easily affected by noise and the location of applied force. And some prior art would install the stain gauge at the cave of the neck portion to overcome this problem. This also will reduce the stiffness of the spanner and the spanner will break at the neck portion. Thus there is an eager demand for a novel design which can improve the defect in the prior art.